The present invention relates generally to air conditioners, and in particular to a system and method for controlling the starting of an air conditioner that employs a pulse width modulated compressor.
With the enlargement of buildings, there is an increasing consumer demand for a multi-air conditioner in which a plurality of indoor units are connected to a single outdoor unit. In such a multi-air conditioner, the length of each refrigerant conduit connecting each indoor unit to the outdoor unit is long because the outdoor unit is relatively far away from the indoor unit, so the amount of filled refrigerant is large and liquid refrigerant can enter the compressor during the starting of the air conditioner.
In particular, if power supply to any indoor unit is abruptly cut off during the operation of a multi-air conditioner, there is increased a possibility that liquid refrigerant enters the compressor. When the power of an indoor unit is abruptly cut off during operation, an electronic expansion valve is not closed because power supply to the electronic expansion valve constituting an element of the indoor unit is cut off. Accordingly, high pressure liquid refrigerant situated in a refrigerant conduit between the condenser and the electronic expansion valve enters the compressor or an accumulator upstream of the compressor through the electronic expansion valve and the evaporator in a non-evaporated state.
This phenomenon is continued until the pressures of high and low pressure sides are balanced. The liquid refrigerant having entered the compressor is mixed with oil contained in the compressor to dilute the oil, so the lubrication of the friction portions of the compressor is deteriorated, thereby damaging the compressor.
Meanwhile, for the multi-air conditioner, a great cooling capacity is required and each indoor unit is frequently turned on/off, so the required cooling capacity is changed. In order to meet such a demand, a variable rotation number compressor having a large and variable capacity is employed in the multi-air conditioner. In such a variable rotation number compressor, the capacity of the compressor is regulated to be suitable for a variation in required cooling capacity in such a way that the rotation number of a motor is controlled by varying the frequency of current applied to the motor in an inverter control manner. However, the conventional variable rotation number compressor is problematic in that the rotation number of its motor cannot be controlled with a desirable response and a precision because the motor being rotated has to be controlled directly according to a required cooling capacity. Additionally, since the rotation number of the motor is frequently varied, vibrations and noises occur, thereby causing problems that the life spans of the motor and the compressor are shortened and the mechanical reliability of an entire system is deteriorated.
In addition, since an expensive and complicated circuit device is required and power consumption is great in order to vary the frequency of current applied to the motor, the conventional variable rotation number compressor is less efficient than a general compressor. Particularly, in the conventional variable rotation number compressor are required several power conversions of initially inputted commercial AC power into DC power and this DC power into AC power having a required frequency through converters, so the structure of the circuit device is complicated and noises are frequently generated in the circuit device.
In addition, a large-capacity, variable rotation number compressor is problematic in that it is difficult to control the compressor, the efficiency of the compressor is low, the size of the compressor is large and the cost of the compressor is high, so it is difficult to fulfill large-capacity requirements with the variable rotation number compressor. Accordingly, in order to fulfill a large capacity requirement two or more compressors are employed. In this case, a standard compressor in which its motor is rotated at a constant speed is generally utilized together with the variable rotation number compressor. If a plurality of compressors are utilized, the entire size of an outdoor unit is enlarged and, accordingly, the handling of the outdoor unit becomes difficult.
Pulse width modulated compressors are disclosed as other variable capacity compressors in U.S. Pat. No. 6,047,557 and Japanese Unexamined Pat. Publication No. Hei 8-334094. These compressors are utilized in refrigerating systems each having a plurality of freezing compartments or refrigerating compartments, and designed to be applied to short piping in which the portion of a refrigerant conduit situated between a compressor and an evaporator is short. Consequently, these compressors cannot be directly applied to air conditioning systems for buildings that indispensably employ long piping and are given control environments different from those for the refrigerating systems. Additionally, in the prior art, there is not disclosed a control system and method for utilizing a pulse width modulated compressor in an multi-air conditioner, and in particular a control system and method for rapidly and safely performing the starting of an air conditioner, preventing liquid refrigerant from entering a compressor during a starting operation or connecting starting and normal operations smoothly.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a system and method for controlling the starting of an air conditioner employing a pulse width modulated compressor, which is capable of rapidly and safely performing the starting of the air conditioner.
Another object of the present invention is to provide a system and method for controlling the starting of an air conditioner, which is capable of preventing the inflow of liquid refrigerant in the air conditioner employing a pulse width modulated compressor.
A further object of the present invention is to provide a system and method for controlling the starting of an air conditioner employing a pulse width modulated compressor, which performs the starting operation of the compressor at two stages, thereby allowing starting and normal operations to be smoothly connected.
In order to accomplish the above objects, in accordance with the principles of the present invention, a system for controlling the starting of an air conditioner comprises a compressor controlled in a pulse width modulation manner according to a duty control signal; an electronic expansion valve for expanding refrigerant compressed in the compressor; a high pressure conduit connecting the exit side of the compressor and the inlet side of the electronic expansion valve; a low pressure conduit connecting the exit side of the electronic expansion valve and the inlet side of the compressor; a bypass conduit connected at its first end to the high pressure conduit and at its second end to the low pressure conduit; a flow rate regulating valve mounted on the bypass conduit for regulating a flow rate of fluid flowing through the bypass conduit; and a control unit for controlling the electronic expansion valve, the flow rate regulating valve and the compressor to perform two stage starting operations in such a way that the flow rate regulating valve is opened and the electronic expansion valve is closed in a first starting operation, and the flow rate regulating valve is closed and the electronic expansion valve is opened in a second starting operation, and the compressor being controlled by a duty control signal having a period shorter than a period for a normal operation during said starting operations.
In accordance with another aspect of the principles of the present invention, a method for controlling the starting of an air conditioner having a compressor controlled in a pulse width modulation manner according to a duty control signal comprises determining whether a starting signal for the compressor is inputted; operating the compressor for a predetermined time period at a period of duty control signal shorter than a period of duty control signal for a normal operation while closing the electronic expansion valve and opening a flow rate regulating valve positioned on a bypass conduit connecting exit and inlet sides of the compressor in a first starting operation, when the starting signal is inputted; and operating the compressor for a predetermined time period at a period of duty control signal shorter than a period of duty control signal for a normal operation while opening the electronic expansion valve to a predetermined extent and opening the flow rate regulating valve in a second starting operation.